<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <!-- 行内式 -->
    <!-- onclick="  "表示点击事件 
          alert表示js弹出框
    -->
    <button onclick="alert('666666')">点击登录</button>
  </body>
</html>
